Brake force regulators, as well as all other valve devices forming part of a fluid pressure operable brake system, are subject to leakage tests as part of periodic brake inspections as may be prescribed by law. Vehicle load responsive brake force regulators of the conventional type having "empty", "half", and "load" positions must also be checked for leakage. In this type of brake force regulator, the several positions can be set by hand if the brake force regulator is operably controlled by deflection of conventional leaf or coil springs.
A presently known method of brake-force regulating of vehicles having pneumatic or mechanical springs, with hydraulic axle balancing, utilizes a control pressure, the degree of which is determined by the springs on both sides of the vehicle, acting on opposing pressure areas of equal size on an operating piston of the brake force regulator via respective connections. Since there are two control pressure connections in this type of brake force regulator, two connections to the test pressure must be made when conducting a leakage test. This necessitates the removal of two protective caps so that two test pressure hoses may be connected to the regulator. In using such apparatus, it is possible that one of the hoses may be inadvertently left connected, thereby resulting in false test results.